It is known to provide machines, generally referred to as grinding machines, which are capable of grinding especially finished or fine grinding and honing of spaced-apart regions of a rotatable elongated workpiece such as the cams of a camshaft used in an internal combustion engine.
Such machines can comprise a workpiece support for rotating the workpiece and including, for example, a head stock and, if desirable, a tail stock, between which the workpiece is rotatably mounted on centers, and a tool carrier which has a plurality of grinding stones spaced apart along the axis of rotation of the workpiece and engageable with the respective zones, e.g. the cams of the workpiece to be finished.
The head stock can be provided with a drive for rotating the workpiece and the tool carrier can be formed with means for pressing the stones against the zones of the workpiece to be ground.
In the past, the means for pressing the stones against the workpiece have included a positioning motor or servomotor for displacing the workpiece holders along guides extending parallel to the axis of rotation of the workpiece, these holders being driven simultaneously by the aforementioned motor.
The system thus allows, as the stones are displaced parallel to the axis, a finished grinding of a number of zones of the workpieces so that all of these zones are formed with surfaces which are as parallel to the axis of the workpiece and thus the rotation axis as may be possible.
The guide elements along which the workpiece holders are shifted generally are rails and the workpiece holders are slides or are formed with slides which are displaceable along these rails with the usual travel play.
The slide displacement is effected by the positioning motor which can be a piston-and-cylinder arrangement and has its moving member displaceable in translation. This displacement is effected in the direction in which the workpiece holders are to be moved, i.e. parallel to the workpiece axis and hence the axis of rotation.
This requires for displacement parallel to the axis, proportionately long slides and associated with slides of increasing length, is an increasing danger of tilting of the slide because of the travel play of the slide which is required.
If, of course, the zones to be ground are relatively close together as is increasingly the case with modern internal combustion engines for automotive vehicles, the length of the slides may preclude simultaneous grinding of all of the surfaces.
In the latter case, the machining operation may require a number of machining steps with groups of cams of a camshaft being machined (ground) simultaneously but at different times from other groups of such cams or zones.
This, of course, results in further loss in precision.
In general, it is a significant disadvantage for modern computer-controller and numerically-controlled machinery that a given operation may require several steps at time-spaced intervals.
It is, therefore, the principal object of the present invention to provide an improved grinding machine for elongated workpieces having a multiplicity of axially-spaced zones to be ground whereby the aforementioned drawbacks are avoided.
Still another object of the invention is to provide a machine for the purposes described in which the workpiece holders can be as narrow as possible (as measured parallel to the axis) without introducing the danger of canting and like movements which might introduce inaccuracies, say that the holders can follow close on one another and thereby allow closely spaced zones or surfaces of the workpieces to be measured in a single operation.
Yet another object of the invention is to provide a grinding machine, especially for the fine or finished grinding or honing of cams of a camshaft of the type used in modern internal combustion vehicle engines, i.e. where the zones to be ground are relatively closely spaced.